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Government of South Australia

Northern and Yorke Natural FACT SHEET NO. 4.007 Resources Management Board

June 2011

NRM Plan Managing Acidity CONTACT in the Northern and Yorke NRM Region

Main Office The Northern and Yorke Natural Resources Acid occur from the lucerne flats of Northern and Yorke NRM Board Management region has a range of Marrabel, through the intensive cropping PO Box 175 naturally acid soils and these soils are and grazing areas near Clare, Farrell 41-49 Eyre Road prone to further acidification under certain Flat, Spalding to Jamestown and the Crystal Brook SA 5523 agricultural management practices. Southern Flinders Ranges from Beetaloo to Ph: (08) 8636 2361 Wilmington. Some small areas of acid soils Fx: (08) 8636 2371 The area of agricultural land in the region exist on Yorke Peninsula. www.nynrm.sa.gov.au with acid soils is approximately 270,000 ha or 13% of the region. The area affected by Preventing acidity is increasing under agriculture. As soils acidify plant growth and yields Acid soils are found in the higher rainfall decline, declines, microbial districts which have higher of activity declines and nutrient imbalances nutrients in the soil, on lighter textured soils become evident. It is much more efficient which have little or organic matter to and effective to treat soils for acidity before buffer the acidifying effects and in areas these problems occur. which have a history of high production, legume growth and / or nitrogen See Figure 1: Prevention is the best fertiliser use. strategy

Soil acidity is a condition of soil where Reduced there is an excess of hydrogen ions • Poor plant growth and reduced present and is measured by pH. Soils can productivity – plants which are vary in pH down the soil profile. Acidic sensitive to acidity will decline in soils are usually more acid near the growth and productivity allowing surface and less acidic, or even alkaline, weeds to increase or reduce soil cover at depth where higher quantities of clay which can lead to soil . Plants can buffer the acidification, or where there sensitive to acidity include canola, may be calcium carbonate present which lucerne, barley, beans, peas, medics neutralises the acid. and wheat. Yields have been reduced by >30% on soils with a pH (CaCl2) 4.5-5.0 in the region. Tolerant plants to acidity include lupins, some wheats, triticale, oats and sub clovers.

Figure 1: Prevention is the best strategy Start when below Target Soil pH Target pH Target pH level CaCl2 Water Extensive grazing* 5.0 – 5.5 5.8 – 6.3 Intensive grazing / Cropping* 5.5 6.3 Vines / Olives 5.5 – 6.5 6.0 – 7.0 *Target can vary with treatment of surface soil acidity or subsurface acidity Government of South Australia Government of South Australia Northern and Yorke Natural Northern and Yorke Natural Resources Management Board Resources Management Board

• Nutrient loss – in strongly acid Increased soil toxicity Off-site effects soils, potassium, calcium and Toxic levels of aluminium and • Increased risk of magnesium can be depleted by manganese – are released into through the reduced amount of leaching or removed in products soil solution as pH (CaCl2) drops soil cover and increased runoff such as hay and grain. A lack of below 5.0. Aluminium (Al) toxicity is with subsequent water pollution calcium can also contribute to a problem when soil extractable Al and deposition in streams. soil structural problems. levels are >2mg/kg or exchangeable • Increased dryland salinity • Nutrient tie-up – nutrients such Al is >5%. Toxic levels affect through decreased plant water as phosphorus and manganese growth and the soil biota. use, increased recharge and can become unavailable as soil subsequent watertable rise in acidity increases (Figure2). Soil structure/clay degradation – the catchment. • Phosphorus inefficiency – strongly acidifying conditions breaks • Increased pollution of phosphorus combines with free down the clay minerals releasing and surface water aluminium and iron released aluminium and iron and damages the due to leaching of nitrate, other in acid soils and becomes less soil structure. Damage to the clay nutrients and heavy metals from available to plants. Molybdenum components of the soil is irreversible. the soil profile. is also less available. • Reduced microbial activity – Stock health – acid soils with low Management of acid soils microbes which fix nitrogen or levels of calcium and magnesium Liming decompose organic matter are can contribute to the risk of grass Lime (calcium carbonate) and other less active in moderately and tetany in grazing livestock liming materials reduce acidity by strongly acidic soils. neutralising the acid reaction in the • Declining land values – loss of soil. The finer liming material with a productive capacity due to acidity higher purity and higher neutralising can reduce land values. value (NV) preferably >80% provides a quicker response. Figure 2: Soil pH and nutrient availability Gypsum does not neutralise acidity.

Prevention is the best strategy Apply lime before productivity is lost so apply when the soil drops below the target pH. Monitor soil pH every 5 to 10 years to determine the timing of the next lime application. Acidification can occur down the soil profile. Check the sub surface layers (10-20cm) if the surface soil (0-10cm) pH is low.

Factors affecting Liming • – sandy soils require less lime than clays to change soil pH. Because of their higher buffering capacity clays take longer to acidify but need more lime to change the pH Government of South Australia Government of South Australia Northern and Yorke Natural Northern and Yorke Natural Resources Management Board Resources Management Board

• Rate of lime applied – in the Other practices to reduce the Grazing remove less alkalinity in region rates vary from 1.0 to 3.0 rate of soil acidification: meat, milk and wool. tonnes per hectare depending • Rates of N fertilisation – high • Claying – certain clays on the soil pH and soil texture. rates of ammonium fertilisers applied to acidic sands to Higher rates can reduce accelerate acidity. For example improve water and soil frequency of applications. Even the use of equivalent amounts nutrient capacity can provide a spreading is essential. Caution: of urea in place of sulphate of liming effect. High lime application rates can ammonia or MAP will slow pH • Fertigation practice – vine induce manganese deficiency change. Match fertilizer use to growers and other irrigators especially on sandy soils expected production so that applying nitrogen fertilisers and • Desired pH range – the lower nitrate is used by plants and not surface water through driplines the soil pH, the more lime is leached from the soil. and sprinklers need to monitor needed to recover ideal levels. In • High percentage of pH and acidification rate within soils where the sub-surface layer leguminous crops and the wetted zone. Liming the (10-20cm) pH is low the surface pastures – grow crops or wetted zone or using calcium pH may need to be maintained at pastures with high nitrogen nitrate as the nitrogen source are a higher level through liming to requirements to utilise nitrogen the best options if the area enable movement of lime into the produced by legume crops is acidified. sub-surface layer. and pastures. • Rate of product removal – hay Further information cuts and intensive cropping systems with high productivity Help and Assistance remove more alkalinity in NRM Authorised Officers grain and hay so the rate of Riverton – 8847 2544 acidification is higher in these Kadina – 8821 1555 paddocks. Monitor the soil pH of Orroroo – 8658 1086 these paddocks more frequently. Figure 3: Spreading lime in the region